A microphone is an acoustic-to-electric converter (e.g., a transducer or sensor) that converts sound (i.e., acoustic pressure) into an electrical signal. Microphones can operate using a number of techniques including electromagnetic induction (e.g., as used in dynamic microphones) and capacitance change (e.g., as used in condenser microphones).
Many microphones being utilized today are condenser microphones, which typically feature a fixed electrode (also referred to herein as the “backplate”) in close proximity to a moveable electrode (also referred to herein as the “diaphragm”). The backplate is typically rigid and is necessary because condenser microphones use electrostatic (i.e., capacitive) transduction between the diaphragm and the backplate to convert acoustic pressure into an electrical signal.
Condenser microphones typically use a small gap between the respective electrodes formed by the diaphragm and the backplate to achieve high signal-to-noise ratios (SNRs), frequently resulting in reliability challenges such as stiction. Such a small gap between the backplate and the diaphragm can also degrade the thermal-mechanical noise performance by damping the overall mechanical structure. Moreover, a DC bias between the backplate and the diaphragm is typically required to enable capacitive detection of motion. However, such a DC bias between the backplate and the diaphragm can be a significant source of power consumption.
A further consideration is whether condenser microphones (e.g., micro-electro-mechanical-systems (MEMS) condenser microphones) can be configured with a top port package configuration (also referred to herein as the “top port configuration”) or a bottom port package configuration (also referred to herein as the “bottom port configuration”). In a top port configuration, a MEMS condenser microphone is typically soldered to a printed circuit board (PCB), and acoustic access to the MEMS condenser microphone is provided through a hole at the top of the package. In a bottom port configuration, acoustic access is provided through a hole in the bottom of the package. A bottom port configuration also generally requires a hole in the PCB to enable sound to reach the MEMS condenser microphone. Although such MEMS condenser microphones can be made in either a top or bottom port configuration, holes must typically be machined into the backplates, increasing fabrication complexity.